AB0228 UTILITY OF SERUM KL-6 IN PATIENTS WITH STABLE OR SLOWLY DECLINING LUNG FUNCTION IN RA-ILD
Authors: S. H. Chang, J. Y. Pyo, S. U. Kim, M. U. Kim, J. W. Kim, Y. J. Ha, J. S. Lee, J. S. Lee, C. H. Park, S. W. Lee, E. H. Kang, Y. A. Lee, J. Y. Choe, Y. Park, E. Y. Lee
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Interstitial lung disease (ILD) is a severe extra-articular manifestation of rheumatoid arthritis (RA). Previously, we stratified the patients with rheumatoid arthritis-associated interstitial lung disease (RA-ILD) into four distinctive groups according to their change of percent predicted forced vital capacity using trajectory analysis: persistently improving, stable, slowly declining, and rapidly declining.<sup>[1]</sup> Till October 2020, a total of twelve patients died, of which eight patients died even though they belonged to either stable or slowly declining groups. Therefore, it advantages additional biomarkers benefits to anticipate poor prognosis. <h3>Objectives</h3> To analyze whether serum Kreb von den Lungen 6 (KL-6) predicts mortality among patients with stable or slowly declining % FVC pred. trajectory group. <h3>Methods</h3> The Korean RA-ILD (KORAIL) cohort is the prospective observational cohort. Patients diagnosed with RA based on either 1987 or 2020 ACR criteria and with ILD based on CT scans had been recruited from six tertiary medical hospitals in Korea from January 2015 to July 2018 and followed for 3 years. Pulmonary function tests and chest CT scans were conducted annually. Serum KL-6 level at enrollment was measured by Nanopia KL-6 assay (SEKISUI, Japan). The cut-off value of KL-6 was referenced in the previous report.<sup>[2]</sup> Kaplan-Meier Log-rank tests and Cox proportional hazard analysis were conducted using SPSS statistics 21.0. <h3>Results</h3> Among patients with stable (n=68) and slowly declining (n=54) lung function groups, three and five patients died, respectively. The mean age of the stable disease group was statistically significantly higher than that of the slowly declining group (64.9±7.7 vs 67.9±6.8-year-old, p=0.03). There was no significant difference between groups in the proportion of males (n=21 vs 19, p=0.70) or ever-smokers (76.1% vs 66.7%, p=0.31), and the mean duration of RA or ILD (RA duration 8.6±8.8 vs 6.7±7.1 years, p=0.21; ILD duration 3.2±3.6 years vs 2.5±2.9 years, p=0.25). Serum KL-6 levels at baseline were comparable between groups (636.3±454.6 U/mL vs 590.6±547.3 U/mL, p=0.62). The hazard ratio for death in the KL-6&gt;1000 U/mL compared with the KL-6 group≤1000U/mL was 3.77 (95% confidence interval, 0.90-15.8, p=0.07) in an unadjusted model and 4.05 (95% CI, 0.68-24.2, p=0.13) in a model adjusted for age, sex, history of smoking (Figure 1). <h3>Conclusion</h3> In RA-ILD, patients with serum KL-6 levels&gt;1000U/mL at baseline tend to have 3.8 times as high mortality as those with serum KL-6 levels≤1000U/mL, although not statistically significant. The current study result implies that serum KL-6 level can be a useful tool to predict poor prognosis even in the case when the lung function of patients is stable or slowly declining. <h3>References</h3> [1] Chang SH, Lee JS, Ha Y, Kim MU, Park CH, Lee JS, Kim J, Chung SW, Pyo JY, Kang EH, Lee YA, Park YB, Choe JY, Lee EY. Lung function trajectory of rheumatoid arthritis-associated interstitial lung disease. Rheumatology (Accepted) [2] Kohno N, Akiyama M, Kyoizumi S, Hakoda M, Kobuke K, Yamakido M. Detection of soluble tumor-associated antigens in sera and effusions using novel monoclonal antibodies, KL-3 and KL-6, against lung adenocarcinoma. Jpn J Clin Oncol. 1988 Sep;18(3):203-16. PMID: 3411786. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.